In an optical communication system, it is generally necessary to couple an optical fiber to an opto-electronic transmitter, receiver or transceiver device and to, in turn, couple the device to an electronic system such as a switching system or processing system. These connections can be facilitated by modularizing the transceiver device. Such optical transceiver modules include a housing in which are mounted opto-electronic elements, optical elements, and electronic elements, such as one or more light sources (e.g., lasers), light sensors (e.g., photodiodes), lenses and other optics, digital signal driver and receiver circuits, etc. In addition, a transceiver module typically includes an optical connector that can be coupled to a mating connector at the end of a fiber-optic cable.
Various optical transceiver module configurations are known. For example, a configuration commonly referred to as “Small Form Factor Pluggable” or SFP refers to a transceiver module having an elongated housing with a rectangular cross-sectional shape, where the rear of the module has an electrical connector that plugs into a bay of a front-panel cage, and the front of the module has an optical connector that accepts an optical fiber plug. Another module configuration, for example, is commonly referred to as “mid-plane” mounting. A mid-plane mountable transceiver module includes an electrical connector, such as a Landing Grid Array (LGA) or a MEGARRAY™, which are mountable on the surface of a printed circuit board. Mid-plane mountable transceiver modules include “parallel” transceivers that transmit and receive multiple optical signals in parallel, using arrays of light sources and light sensors.
As illustrated in FIGS. 1-2, one type of mid-plane mountable transceiver module system includes a transceiver module 10 and an optical connector 12 that attaches to transceiver module 10. Transceiver module 10 includes an opto-electronic system that transmits and receives optical signals (i.e., beams) in a direction normal to the printed circuit board (PCB) 26 that forms the base of transceiver module 10. For purposes of clarity, only a single-laser chip 14 (e.g., a chip having a single vertical cavity surface-emitting laser or VCSEL) of such an opto-electronic system is shown in FIG. 2. Optical connector 12 is user-connectable to a receptacle (not shown for purposes of clarity) on the top of transceiver module 10. When connected to transceiver module 10, a portion of optical connector 12 abuts or contacts the top of a lens block 16 (FIG. 2) of the opto-electronic system. Optical connector 12 includes a reflective surface 18 that redirects the parallel optical signals 20 emitted by laser chip 14 at a 90-degree angle into the end of an optical fiber of a ribbon cable 22. Lens block 16 includes at least one lens element 24 in the path of optical signals 20. Lens element 24 collimates the beam or optical signals 20 emitted by laser chip 14.
The accuracy of the spacing or distance D shown in FIG. 2 between laser chip 14 and lens element 24 is critical. If the distance D is too large or too small by even a small amount the beam will not be collimated properly, and signal integrity will be impaired. At least two mechanical tolerances can affect the distance D. Both lens block 16 and laser chip 14 are commonly mounted on the same substrate, such as PCB 26. The height H of laser chip 14 has a tolerance that can affect the distance D. Also, as laser chip 14 is commonly mounted on PCB 26 using an adhesive layer 28 (e.g., epoxy), the tolerance of the thickness of adhesive layer 28 can affect the distance D.
It can further be noted that the force exerted by optical connector 12 against the top of lens block 16 can undesirably displace lens element 24 by a small but optically significant amount, potentially adversely affecting the optical alignment (e.g., the distance D). Excessive force can even potentially crack a lens block 16 made of fragile optical glass.
It would be desirable to provide an optical communication module having a lens arrangement that helps minimize the adverse impact of mechanical tolerances and forces.